Process of manufacturing sulfite fiber and recovering sulfur dioxid



J. P. V. PAGAN, H. G. SPEAR AND R. B. WOLF.

PROCESS 0F MANUFACTURING SULFITE FIBER AND RECOVERING SULFUR DIOXID.

APPLICATION man APR. so. |918.

1,327,666, Patented Jan. 13, 1920.

R E w A UNTTED STATES 1%',15143, NT-joEnron.i

JAMES P. V. FAGAN, HERBERT G. SPEAR, AN'D ROBERT 13;. WOLF, BERLIN,HAMPSHIREiSAID FAGAN AND SAID SPEARASSIGrNORSl 0F' THEIR ARIGHT T0 BROWNCOMPANY, 0F BERLIN, NEW HAMPSHIRE, A CORPORATION OF IIMIAINE.v

PROCESS or MANUFACTURING sULFI-TE FIBER AND REeo'vEEING SLFUE DIOX'ID:

To all wkom t mayl concern ABe it known that we, JAMES P. V. FAGAN,HERBERT G. SPEAK, and ROBERT B. WOLF, citizens of the United States,residing at Berlin, in the county of Coos and State ofv coveryrof SulfurdioXid in connection with the digestion of wood in the manufacture ofsulfite liber.

The invention consists in liberating from the upper portion of .thedigester the gases and steam which areordinarily liberated in the blowpit, and byl condensation eliminating the water and other condensablegases, and finally separating from kthe remaining inert gases, e. g.nitrogen, oxygen and carbon dioxid, and recovering substantially puresulfur dioxid. l v

Itis customary` in the usual practice of cooking the chips in a calciumbisulite solution containing free sulfurous acid, occasionally or fromtime to time to relieve the digester of the air and gas atthetop thereofthrough a smallscreened relief pipe, and, after the cook is completed,yto blow the contents of the digester into a blow pit, and

to permit the steam'and gases constituting a part of such contents toescape into the i atmosphere through the vomit stack leading' from theblow pit. l According to our present invention, we employ, in additionto the usual rellef system, a relatively large and preferablyunobstructed or unscreened conduit which ,cara

-ries the vapor and 'gases (which usually, are* liberated in the blowpit) from the upp'erf` Y of which leads a small screened and valved pipe2 for permitting the usual relief durpart of the digester `to acondenser .during the completion of the cooking operation, or,

if so desired, during the whole cooking.

period. These vapors and gases, having a boiling point at 212C. F. andabove, are con` densed, and the remaining gases are .then treated torecover the sulfur dioxid in any f Asuitable way, as fori example by.conducting them through a lime tower wherein the sulfur dioXid isrecovered inthe forni of cal'- cium bisulite.

. l .Specicationof Letters Patent.`

Preferably there is' rinterposed between the condenser and thedigester*A n Patented Jan."13 ,192o. 'Applicationmedaprnao,191s.serial'N'azalzaA l a Settling or ycollector chamber in which any Y pulpand liquor escaping through the conduitv is caught and collected, This.we in'd -f to be desirable, as the/ conduit Inus't be rela-,

tively unobstructed, andV consequently, as

previouslyindicated, no screen is employed, Y, I

therein asin the usualrelief pipe leading fromV the top of the]digester. After the valve of the-gas blow pipe or conduit lead' ing fromthe topV orupper portiony of the digester has been opened and while itis yet only cracked, we preferably inject sutlicieit steam into thedigesterQfrom below lto cause .I

yan ebullition'of the mass and to insure the escape of most of thesulfur dioX-id gas that may be/left therein, during which time, even Ythoughe gases and steam are escaping through the cracked valve,`r thepressure continueato increase until ythere is suicient pressure to` blowthe digester, since the steam, is ad,-

mitted faster at the bottom than it is relieved at thetop. During allthis period,

the completion o'f the cooking operation may proceed, f and consequentlythe 'recovery of the sulfur dioXid may beaccomplished during` suchperiod. The final' injection-.of

.steam asthus describedinay therefore a part of the cooking yoperation"an jl nota steph following the completionl thereof, since the injectionof steamat a pressure necessary ,to blow`the digesterafter the cookingisiinished might causean .overcookingof the material'l but, instead ofemploying steam for blowing the contents of the digester, we

`may employait` drawn from a storage tank p in which it iscompressed 0'1. Referring now to the accompanylng drawing, ,whichillustrates,conventlonally an ap-` paratusrfembodying the invention andby means ,of which` ourwprocess may be prac-l tiSed,-1 illustrates.a-digester from the top ing the crookim'g. 3 indicates a b low'pithaving a'targetA and vomit stack 5 and prolvided with the .usual falsebottom (mdicated dotted lines) for draining the hquor the wood chipsunder the pressure and at l, tothe removable top 14 of the digester asillustrated. The pipe is connected to a main of larger diameter, towhich other similar pipes leading from other digesters may communicate.16 indicates a relatively large v"collector or settling chamber. Thefunction ofthis chamber is to collect the pulp and liquor, which settlein the lower y portion, and which may be discharged therefrom by anoutlet 17 having a valvelS, into I the blow pit 3. If desired, the pulpand liquor may be delivered by the outlet pipe to the blow pit or to astorage tank (not shown). The settling and collecting chamber isconnected by a conduit 19 with a sur- .y face condenser indicated as awhole 'at 20,

such an extent as to absorb any .appreciable the sections of which areconnected with' an upper manifold. 21 and with a lower manifold 22lwhich forms a drip and settling chamber, Said chamber 22 has an end 23which is removable for cleaning purposes. The coils 24 for the coolingmedium are conventionally shown byv dotted lines, the inlet and outletbeing indicated respectively at 25 and 26. Water at seasonabletemperatures is employed as the cooling medium, and is caused to flowfrom the topf'to the bottom so as`not to cool the waterofcondensation'to quantity of gases. This water of condensation isdischarged from the condenser into the collectin chamber 22 and'lowstherefrom throug drip pipe 27 to the tank 28. The manifold 21 isconnected by a. pipe .29 to any suitable apparatus for absorbing orotherwise recovering sulfur dioXid. A lime tower 30 is illustratedforfthe purpose referred to, and a pipe 31 leads from the top thereof toya vacuum pump 32. The discharge pipe 33 from. lime tower 30 leads tothe acid storageltank, 34.

At the top of the vomit stack 5 there is a movable luted cover 35 whichmay bel opened to permit'the escape of vapors and gases to theatmosphere, but said stack is connected by a by-pass 36 to the conduit19, and is also provided with the valves 37 38, for cutting off the Howof vapor through the stack entirely, or `for causing its diversion Ythrough the condenser, if desired.` When' both valves are open, thevapors pass directly to the atmosphere, 'the cover being lifted forthispurpose.

y acid. Steam is injected from time to timev through the "valved inlet 9to cook the mass at the desired temperature under the desired pressure,and from time to time the valve of the relief pipe 2 is opened to permit the escape of air and some of the gases, in accordance with theusual practice.

'When the cooking process has so far progressed that the remainingoperation to be described will complete it, the pump 32 is set inoperation to create a vacuum in the tower which is exerted lthrough thesystem back to the digester, and the valves 12 and .13 are openedl Atthis time the valves 18, 37, v38 are closed. The gases and vapors, withmore or less liquor and pulp, blow through thev pipe 10 and main 15 tothe settling chamber 16, until finally there is a reduced pressure orpartial vacuum in the digester. The vapors, in passing through thecondenser 20, together with the gases which condense at a temperatureslightly below are condensed and drop into the tank 28, and are therecollected with the small amount of liquor and pulp which passed overfrom the digester. The sulfur dioXid, and the other gases, consistingmainly of nitrogen and carbon dioxid, are drawn from -the condenser bythe pump 32 into the tower or absorbing system 30 where the sulfurdioXid is absorbed and recovered-in this case in the form of calciumbisulfite.

During the completion of the cooking, the valve 13 is partially closed,or crackedf and steam is injected again into the digester to cause thecirculation of the contents of the lower part of the digester (whichowing to the static head of the liquor'above it will not liberate gaseasily) to the top thereof to insure the liberation and discharge of anyremaining sulfur dioxid, and to prevent the digester from packing. Thenthe p-ressure in the digester is brought to the desired degree, theycontents may then be blown in the usual manner into the blow pitagainst the target, and the liberated steam (which is now free of sulfurdioXid) escapes through the vomit stack.

7e consider it desirable to have the cooling medium pass through thecondenser in such Way that the products of condensation are at a hightemperature `to prevent the ab- .sorption thereby of the sulfur dioxid,and it is for that reason that we carry the coil 24 v35. fromthedigester. v

rlhe process as described is ldifferent from We could,'offcourse,dispense with-the separate small relief pipe, and, 'during the Icooking, relieve the di ster through the large unobstructed lcon uit 10by slightly openingthevalves 12 and 13,andv we'should \15 not regardthis elimination of the smallre.-

,lief ipe in vsuch caseas a departure yfrom the. invention. IIn orderthat thel gas-andv'apor blowing operation, which completes. l thecooking operation, should take `a rela- .'20 tively short time-say, tento twenty minutes-'the discharge conduit should be lunobstructed andshould be several times larger than the relief pipes which haveheretofore been employed.

1 Insteadgof building up the pressure inl the digester'by the injectionof steam through the pipe 9, we may (after blowing suilicient steam intothe digesterL contents while the valve 13 is cracked) fdo so by forcingf steam through vpipes 40, 39, linto the top of the digester, or byforcing air,l thereinto from the tank 42 through pipes 41, 39,especially when the cook has been completed by tlietimethe SO2 gas has'all beeny liberated that heretofore followed, in which the dii vgester. is relieved from time to time through vthe usual .relief systemwhich includes instru- 40 mentalities for the recovery ofthe as andliquor, because 'in such case the relie pipe is relatively small indiameter andfis screened,

and the purpose of the relief is to permit the Iesca e of air and' onlyenough steam 4 5 permit the, injection of livex steaml into the lowerendof the'digester to maintain the vcontents at the .proper cookingtemperature,

and because the subsequent blowingof. the digester causes .theliberation and wastage through the blowl pitand vthe vomit stack' .ofvastquantities of sulfur dioxd into the-' surroundingatmosphereQAccording tto the present invention; on 'the other hand, the discharge"o f ractically all the ,gases-land '55 the recovery o rthelsulfurcdioXidare effectedl lprior tothe blowing of the Idigested.material into theblow pit..` `This v i s practically assured by causinga vacuum -in therecovery piped to connectwith'gthe' v main 155,or the system. may beconnected-to only'` a small Itis qulte. evident that the recovery system-may be practically-in'continuous operation, when'it constitutes `apartj of va large installation comprising number of digesters,

number of digesters. 4A system such as here- 1n describedpossessesnumerous advantages which will 'be appreciated by those skilled in theart, among which may be briefly mentioned',- l

l First, the ease of its installation and ,its

low cost of constructionv and maintenance; l Second, fthe possibility ofrecovering almost `the last trace of sulfur ydioXid from the cookingliquor during the cookingoperatim without loss of production ormaterial; an l Third, an increased yield per day from the digesters,vdue to the rapldgas.' recovery l during the cooking process.

T o one familiar with the m'anufa'ctureof sulite Pfiber, other manifestadvantages of `the process and apparatus hereinbefore described willrbeapparent.` It may not be amiss, however, to `point vout that we. are

thereby enabled to obtain a practically pure sulfur dioxid, assubstantially all air leaks,

which are` 'necessarily present ina large system of piping, arepracticallyeliminated. Furthermore, inasmuch as the digesterjisair-tight and it -isvery `diilicult to lprevent the access of air to andits accumulation in the blow pit, bypassing the vapors directly fromthedigester to the recovery system 'and not through the blow it,- weeliminate the further danger of air" ing drawn into the recovery system;By eliminating the danger of airbein'g drawn into the recovery system,we prevent the formation of 'calciuml sulfate in the lime, tower andobtain an acid rich in SO2.v Another advantage, due to the process vand'apparatus, is that we may employ a relatively small surface condenser,since a longer .time may be taken forblowing off the 'vapors and gasthan where vthe entire contents of the digester are blown into the .blow

j pit. Further, we .save wear and tear on the low pits, since the gas islargely prevented fromreaching them. 1

' 'A further advantage of this process is that `it` permits the contentsof a digester to be held, without overcooking. It frequently Yhappens amill thatthe cooking in a givendigester progresses" to av point wherelit is :necessary to blow 'the' contents into the 'emptied lfrom thematerial resulting' from a .blow pit, but, because the pit 'has notbeenprevious blow, it is advisable or desirable to delay the blowing of theldigester. This could ynot be doneunder .ordinary conditions asl thematerial would be spoiled by overcooking.I Butaccording toour 4processand system, the digester may be/blown free of l gas landl 'steam and thetemperature of the contents reduced to a point where no cookingtakesplace, and the digester held until the' blow pit is free to beused. T hecontents of the digestengthough hot, are still incompletelycooked,`and may beheld in the digester for a reasonable length of time,until the steam is again injected to bringlthe'pres-v sure to a blowingpoint, thus comp eting the cook, all without any deterioration of thefiber; or else, if the cooking has beengcompleted, air may be usedtobuild up the pressure suiciently to blow the chips and liquor into theblow pit. y

One may, fif desired, permit the vapors landgases to pass from the blowpit through said invention, and described a way of making and using thesame, although without attempting to set forth all of the forms in whichit may be made or all ofthe `modes of its use, what we claim is':--`

1. Theherein described process of recovering sulfur dioxid andA in themanufacture of sulfite pulp, which consists "in blowing into acondenserY from the top of the digester,

at or during the last portion of the 'cookingV operation, thosevaporsand gases'which are usually blown with the digester contentsinto theblow pit, andseparating and-recovering sulfur dioxid Vfrom such vaporsand gases.

2. The herein described process, which consists in cooking chips yunderheat and pressure in acid' liquor in a digester, before the cookingoperation is completed'blowing from the to of the digester those vaporsand-gases w 'ch are usuall .blown withthe digester contents into the bow pit, eondensing the vapors, and separating and recover'- -ing sulfurdioXid froml the remaining gases.

3. The vherein described processf which consists in'pa-rtiall cookingthe raw 'material and then, comp eting'the coolngp'perw' tion whiledischarging from 'the top of the,` rs which are digester those gases andva v usually blownl into the blow plt'wlthfthe digester contents,increasing -the pressure; 1n

the digester, then blowing the digester-contents into the blow pit, andAseparating and recovering sulfur dioxid from the` said va,

pors and ses. Y v

LL'The herein' described process, which consists in partially cookingthe raw material, and then, during'the completion of the cookingoperation, discharging; the gases and vapors from the top ofthe digesterinto a recovery system wherein the contained sul` fur dioxid isseparated and recovered and at the same time injecting steam rinto thelower portion of the ldigester to insure the; discharge ofthe dioxldthe` com-A I gases are blown through the ,con-A pletion lofthe cook, andfinally blowingthe v digester contents practically free of sulfur dioxidinto the blow pit.

5. The herein described process l,which consists in cooking the rawmaterial in the usual manner and relievingthe pressure as ordinarily,then, when the cooklng is substantially or nearly completed, dischargingfrom the upper portion of the digester into a conduit, in which thepressure is below ati mospheric, those gases and vapors which l areusually blown' with the cooked material into the blow pit, condensingthe vapors, and separating land recovering sulfur dioXid from theremaining gases, injecting steam into the digester and partially closingsaid conduit, and finally, when the pressure 'is sufficient, blowing thecooked material practicallyfree of sulfur] dioxid from the lower l endof the digester into a blow pit.

6. The herein 'described process which consists in cooking the rawmaterial-in the 'sulte liquor ina digester under conditions of heart'and pressure, on partial or' substantial completion of the cookingoperation disn charging all the contained gases and vapors from theupper portion of the digester intoa conduit `held under 'reducedpressure, sep-l arating therefrom-the pulp and liquor carried over"therewith, condensing the vapors byvsurface' condensation, separatingand` recovering the 'sulfur dioxid from the remain- Y ing gases,partially closing said conduit and forcing an elastic Huid into theVdigester to ree the contents'y thereof of sulfur dioxid and tobuild upthe pressure in the digester,

yand .finally-by such pressure blowing the contents ofithe digesterpractically free of sulfur dioxid intoa` blow pit.

7. The herein described processl for the y"I nanulacture of sulfitefiber, which consists 1nl cooking the raw material in the usual.manner,- relievinglthe ldigester fromtime t0:

time as ordinarily, Mld .there when the 000k;

ing operation nears completion," blowing the vapors and gas from theupper ortion of the digester substantially at orbe 0W atmosphericpressure, and recovering the gas, then forcing ran elastic medium-`underpressure ,-into the upper'portion of the digester, and forcing'the cooked material under pressure from'vthe lower end offthe digester.

8. The combination of a digester, a blow pit, a surfacecondenser, arecovery apparatus fr for gasconnected to the condenser,

and a large unobstructed discharge pipe for?,

conducting the vapor and gas, upon comple` tion-'of the cookingoperation, from 'the up` J per portion of the digester to saidcondenser.. and recovery apparatus for the condensation of the vapor andrecovery of the gas. 9-. The combination ofa digesterhaving valveddischarge 4pipe leading from the upper end thereof, ablow` pit,afconduit leading from `the' lower end of the vdigester to` the blowpit, a vacuum pump, a surface condenser and a gas-recoveringinstrumentality interposed between the valved discharge pipe and thepump, in consequence of which, during the completion of the cooking ofthe raw material, the gases and vapors may be discharged through saidpipe, the vapors condensed land the sulfur dioXid recovered.

10. The combinationl with a digester hav-h ing the usual valved reliefpipe, a blow pit, and a conduit leading from the digester to the blowpit, of a relatively large valved conduit leading from the upper portionof the digester, a settling chamber, a surface condenser, and agas-recoverlng instrumen- .tality all connected with the said conduit inthe order named.

11. The combination with a digester having. the usual valved reliefpipe, a blow pit,

and aconduit leading from the digester to the blow pit; of a relativelylarge valved conduit leading from the upper portion of the digester,asettling chamber, a surface condenser, a gas-recovering instrumentality'all connected with the said conduit inthe'v order named, land a vacuumpump for creating a Vacuum back to the digester in the digester duringthe cooking operation, of a y large size unscreened discharge conduitleading from the upper portion of the digester for the discharge of thegas and the digester hav` I relief liquor in the form of vapor, asurface condenser for condensing the vapors, a pulp and liquid separatorin said conduit interposed -between the condenser and the digester, avacuum pump, and a gas recovery apparatus interposed between the pumpand the condenser, said parts all being so arranged that, prior to thedischarge o f the cooked material from the digester, apart of the liquorand its contained gas may be drawn. from the digester, the vaporscondensed and the gas recovered.

In testimony whereof We have affixed our signatures.

